class Node:
    def __init__(self, value):
        self.value = value
        self.left = None
        self.right = None
        self.height = 1   # height of a leaf is 1


def height(node):
    return node.height if node else 0


def balance_factor(node):
    return height(node.left) - height(node.right)


def update_height(node):
    node.height = 1 + max(height(node.left), height(node.right))


def rotate_right(y):
    x = y.left
    t2 = x.right

    x.right = y
    y.left = t2

    update_height(y)
    update_height(x)
    return x                  # x is the new subtree root


def rotate_left(x):
    y = x.right
    t2 = y.left

    y.left = x
    x.right = t2

    update_height(x)
    update_height(y)
    return y                  # y is the new subtree root


# Manually build a left-left heavy case: 30 with left child 20,
# which itself has left child 10.
root = Node(30)
root.left = Node(20)
root.left.left = Node(10)
update_height(root.left)
update_height(root)

print(balance_factor(root))    # 2 - unbalanced
root = rotate_right(root)      # fix it with a single right rotation
print(root.value, root.left.value, root.right.value)   # 20 10 30
print(balance_factor(root))    # 0 - balanced again